Anarthria, ALS and locked-in syndrome (target populations)
The clinical populations speech BCIs aim to help: people who have lost the ability to speak intelligibly while cognition remains intact. Anarthria is the complete loss of the motor ability to articulate, for example after a brainstem stroke, and dysarthria is its partial form. Amyotrophic lateral sclerosis (ALS) progressively paralyzes bulbar and limb muscles, and locked-in syndrome leaves a person aware but able to move little more than the eyes.
Crucially, in many of these users the speech motor cortex remains functional and its attempted-speech commands remain decodable, which is the founding premise of the entire field.
As ALS advances, even the residual eye movements used by eye-trackers and switch scanners can fail, making an implanted speech BCI potentially the last reliable communication channel, which sharpens questions of consent, expectation and end-of-life care.